Testing of pandemic ventilators under early and agile development

Aiming to address clinical requirements subsequent to SARS-CoV-2-related pulmonary disease, multiple research groups and industry groups carried out intensive studies to develop pandemic ventilators (PDVs). In vitro testing to critically evaluate the specific performance of the developed apparatuses is an essential requirement. This study presents a test protocol which promotes a test-oriented, iterative, and agile assessment and consecutive development of such PDVs. It allows for fast identification of specific characteristics of each PDV in the individual test features. The test protocol includes an evaluation of the accuracy of control systems and instruments at changing parameters, the oxygen dynamics, and the response to trigger signals. The test environment is a mechanical lung, which allows reproducing various lung mechanics and to simulate active breathing cycles. A total of three PDVs that are under development were iteratively tested, with a Hamilton T1 as a reference. Continuous testing of the PDVs under development enables quick identification of critical application aspects that deserve further improved. Based on the present test protocol, the ventilators demonstrate a promising performance justifying continued development.

The tested patient tubing system consists of a double lumen tube with a mass flow sensor and an integrated pressure sensor at the distal end of the tube. The tubing system is connected to two standard ports; for the intake of fresh air during inspiration and the exhaust of exhaled air.
Supplementary Figure 2 Schematic representation of the operating concept of the girvent. The system can be operated either with low pressure O2 or with high pressure O2. The low pressure O2 is injected into the patient circulatory system via a reservoir, while the high pressure O2 is added via a throttle valve. A PID cotnroller regulates the applied pressure via the pressure sensor attached at the patient tubing system.

Controls and monitoring BASIC CONTROLS
The parameters on the Grivent are set using analog rotary dials. Five parameters can be set on the ventilator; the plateau pressure can be set from 15-35 cmH2O, the PEEP can be set from 2-15 cmH2O, the respiratory rate can be set from 5-30 bpm, the I:E ratio can be set from 1:1-1:3, and the trigger sensitivity can be set from 0-2 mbar.

PRESSURE-CONTROL MODE AND TRIGGER SIGNALS
At the time of the measurements for the study, the GirVent could be operated in one mode, the pressure-controlled continuous mandatory ventilation (PC-CMV). The pressure generated in the ventilation system (ventilator and patient tubing system) is controlled by an actively controlled solenoid valve. The expiration port of the valve is closed during inspiration and open during expiration. By controlling the opening and closing of the solenoid valve, the PEEP can be actively regulated. The pressure and flow sensor attached at the distal end of the patient tubing system is used for the internal feedback of the PID controller of the turbine blower. The pressure sensor is also used for triggering in assisted ventilation mode. The trigger signal is transmitted via an adjustable threshold through the measured negative pressure drop in the pressure sensor.

OXYGEN SUPPLY
O2 supply can be provided both from a pressure source (high-pressure mode) and admixture of O2 from a low-pressure source via an injector (low-pressure mode). In the low-pressure mode, the O2 source is connected to a standard connection for low-pressure oxygen (0.25 bar). The O2 supplied with the low-pressure port is first distributed into a two-liter balloon reservoir and then aspirated during inspiration. The pressure in the balloon reservoir, hence, the amount of O2 supplied during inspiration, is controlled by the O2 supply flow from the O2 source. In high pressure mode, the pressure source is connected to a standard port for high pressure O2 (max. 4.5 bar). The O2 is injected into the patient tubing system during inspiration via a port on the inspiratory output of the ventilator.

MONITORING
The GirVent has a digital LCD display for monitoring all adjustable parameters. In addition, an analog manometer display continuously displays the instantaneous pump pressure. The digital display has four text lines; i.e. inspiratory pressure, PEEP, respiratory rate, I:E ratio, trigger pressure threshold, O2 supply mode and for error messages or alarms. Further, the following alarms are implemented; inspiratory Paw exceeded or not achieved, end expiratory pressure exceeded or not achieved and failure of electricity or gas supply.

O2 High-Pressure Port
Supplementary Figure 12 Oxygen dynamics tests for the Hamilton T1 (high pressure port). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured at different O2 concentration set in the ventilator user interface (40%, 60%, 80% and 100%). Right: measurement of the t90 time of the high-pressure port with an O2 setting of 100% in the user interface.
Supplementary Figure 13 Oxygen dynamics tests for the HEV (high pressure port). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured at different O2 concentration set in the ventilator user interface (40%, 60%, 80% and 100%). Right: measurement of the t90 time of the high-pressure port with an O2 setting of 100% in the user interface.

O2 Low-Pressure Port
Supplementary Figure 14 Oxygen dynamics tests for the Hamilton T1 (low pressure port). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured of the low-pressure port at an oxygen supply flow rate of 2L/min, 4L/min and 6L/min. Right: measurement of the t90 time of the low-pressure port with an O2 supply of 12L/min.
Supplementary Figure 15 Oxygen dynamics tests for the GirVent (low pressure port 1). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured of the low pressure port at an oxygen supply flow rate of 2L/min, 4L/min and 6L/min. Right: measurement of the t90 time of the low pressure port with an O2 supply of 12L/min. Figure 16 Oxygen dynamics tests for the GirVent (low pressure port 2). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured of the low-pressure port at an oxygen supply flow rate of 2L/min, 4L/min and 6L/min. Right: measurement of the t90 time of the low-pressure port with an O2 supply of 12L/min.

Supplementary
Supplementary Figure 17 Oxygen dynamics tests for the Breathe (low pressure port). The results are based on the last 30s before changing the O2 supply or setting (time window indicated). Left: FiO2 measured of the low-pressure port at an oxygen supply flow rate of 2L/min, 4L/min and 6L/min. Right: measurement of the t90 time of the low-pressure port with an O2 supply of 12L/min.